1. Field of Invention
The present invention relates to a backlight module of a liquid crystal display (LCD), and more particularly, to a light guide plate with a plurality of arc-protrusions on a light incident plane.
2. Description of Prior Art
The design of an LED's backlight is improved along with the improvement of LED's efficiency, from the earliest four-side type into a two-side type, and then into a one-side type, the present technology and the direction of future development focus on a single-short-side type.
With the development of 3D technology, a TV with a 3D display function is also gradually becoming a mainstream. Currently the 3D display modes include shutter (Shutter Glass), polarized FPR (Film-type Patterned Retarder) and other manners.
Shutter-style 3D needs to be achieved by the scanning backlight with a panel pixel scanning. Backlight sources are usually partitioned. LEDs of an edge back-lit style LED light bar are divided into sets to correspond to a plurality of subsections of a screen. When the first frame signal scans the first subsection, the LEDs corresponding to the first subsection are lighted up, and the rest of the LEDs are turned off. When the signal scans the second subsection, only the LEDs corresponding to the second subsection are lighted up. The rest can be deduced accordingly. Such operations are necessary to be conducted for every frame. The display performance of the shutter-style 3D depends on a crosstalk between the subsections and timing setting.
The crosstalk between the subsections related to the backlight mainly comes from the effect of the brightnesses of the different subsections. In the best situation, when the LEDs correspond to one subsection are lighted up, the backlight sources of the other subsections all present a dark mode. FIG. 1 is a side-view of a light guide plate with microstructures of a prior art. It is a common design to dispose saw-shaped microstructures 13 on the light emitting plane 11 of the light guide plate 10. The microstructures 13 on the light guide plate 10 destroy the condition of light total reflection with different geometric shapes. FIG. 2 is a light distribution diagram of a flat light guide plate of a prior art and a light guide plate with wave-shaped micro structures of a prior art. It is clearly observed that the light guide plate with wave-shaped micro structures has a more convergent light distribution than the flat light guide plate, but in practice, it is impossible to restrain the divergence of light with only micro structures.
Further refer to FIG. 3, which is a vertical direction brightness distribution diagram when a common light guide plate with micro structures is lighted up in one LED light source. The width corresponds to the light source (100% brightness) is a point, the width of FWHM (Full Width at Half Maximum; 50% brightness) apparently increases. With further refer to FIG. 4, which is a diagram showing the width of FWHM at different distances from the light source. In a single-short-side edge-lit manner, as the distance increases, the FWHM increases accordingly, which means the crosstalk is more serious at a far side than a light incident side of the single-short-side edge-lit light guide plate.
The prior art prevents the divergence of light by forming microstructures as convex lens with the material of light guide plate per se. However, when improving the convergence of light, the increase of width and height of the light guide plate due to the microstructures is disadvantageous to the backlight structure design.